In many electronic circuits it is necessary to be able to switch a single node connected to a given load between different supply potentials or voltages.
FIG. 1a illustrates such a situation in which the same output node (Vout) is switched between several distinct supply voltages (i.e., voltage V33, voltage V55 or ground voltage). This is a very frequent case in electronics, and especially in the context of FLASH/EEPROM memories. As shown, three switches 1, 2 and 3 are used to switch the output node to one of three supply voltages.
In operating mode it is essential that short-circuits between supply voltages be prevented, since short-circuits generate combinational currents such as illustrated by currents I1 and I2 in FIG. 1a. 
Such combinational currents are particularly prejudicial. First, they lead to a considerable increase in power consumption that makes it impossible to realize portable battery powered applications. Second, they cause components to overheat, which heat must be evacuated from the semiconductor. Third, they may cause the output voltage Vout to temporarily drop, which might impede the operation of the circuit. Actually, considering the transitory voltage drop shown in FIG. 1b, and supposing that the output node is used to set the voltage of a MOS transistor bulk, it is clear that any limited voltage drop can cause a normally reverse-biased N-P junction to switch to direct mode.
Consequently, much effort is made to prevent short-circuits between the power sources and to ensure that the three current paths enabled by switches 1, 2 and 3 are exclusively controlled.
U.S. Pat. No. 6,433,583, entitled “CMOS SWITCH CIRCUIT FOR TRANSFERRING HIGH VOLTAGES, IN PARTICULAR FOR LINE DECODING IN NON VOLATILE MEMORIES, WITH REDUCED CONSUMPTION DURING SWITCHING”, describes a switch used in a FLASH memory for switching two distinct voltages on a single node.
In the environment of non-volatile memories in particular, it is desirable to enable switching of at least three separate voltages on the same output node, while ensuring the complete absence of any combinational current.
In addition, it is desirable to realize such a switching circuit using MOS components having a nominal operating voltage that is limited and, in any case, lower than the highest value of the supply voltages to be switched. The aforementioned U.S. Patent does not address this issue.